This invention relates to sprinkler heads and, more particularly, to sprinkler heads that nutate, or wobble, while they rotate, to thereby minimize the “donut effect” prevalent with conventional rotating sprinkler heads.
Various nutating or wobbling sprinkler head designs have been proposed, examples of which are described in prior U.S. Pat. Nos. 5,381,960; 5,950,927; and 6,932,279. Commonly owned U.S. Pat. Nos. 5,439,174; 5,588,595; 5,671,885; 6,267,299; 6,341,733; 6,439,477; 7,287,710; 7,562,833; 7,942,345 and 8,028,932 provide further examples of nutating or wobbling sprinkler heads. There are potential shortcomings, however, that can nullify the very nutating affect that makes such sprinklers attractive in the first instance.
One problem often encountered with sprinklers of this type relates to stalling at start-up or even during normal operation. Stalling occurs when the water distribution plate of the sprinkler head fails to tilt at start-up, or ceases tilting during operation, thereby simply rotating and distributing a stream particularly susceptible to the “donut effect” where the wetted pattern area is shaped like a solid ring around a dry center. When nutating or wobbling sprinklers operate as designed, the nutating action tends to fill in the pattern in a substantially uniform manner. Thus, it is critical that the water distribution plate reliably and consistently remain in a tilted orientation on start-up and while rotating to achieve the desired wobbling or nutating action.
The stalling problem discussed above has been solved in different ways (see, for example, U.S. Pat. Nos. 5,381,960 and 6,341,733).
Another problem relates to the relatively high speed of rotation of the wobbling sprinkler head. High rotational speeds create the well-known but undesirable “horse-tail” effect that shortens the radius of throw of the sprinkler. While it has been shown that slowing the rotation of the sprinkler using a brake mechanism is effective to obtain maximum throw, completely satisfying solutions to the problem of slowing the rotation speed of a wobbling sprinkler head have yet to be developed. One attempt to slow a wobbling head is described in U.S. Pat. No. 7,395,977.
There remains a need for a wobbler-type sprinkler that effectively and reliably achieves maximum throw radius while maintaining the pattern-uniformity benefits of the wobbler-type sprinkler.